Challenges in Early Warning of the Persistent and Widespread Winter Fog over the Indo-Gangetic Plains: A Satellite Perspective

Abstract

Each year during the season (December–January), dense fog engulfs the Indo-Gangetic Plains (IGP) in Southern Asia, extending over a stretch of 1,500 km, for more than a month disrupting day-to-day life of millions of people inhabiting in the IGP. Increasing atmospheric pollution combined with sufficient moisture available due to the passage of frequent north-westerlies favor fog formation in this region. Trends in poor visibility suggest a significant increase in worsening air quality and foggy days over the IGP. The persistent and widespread nature of the winter fog is strongly influenced by the regional meteorology during winter-time, i.e., a stable boundary layer, cold temperatures, high relative humidity, and light winds. The valley-type topography of the IGP, adjacent to the towering Himalaya, and high concentrations of pollution aerosols/particulates, further favors the persistence of hazy/fog conditions. A satellite- and surface-based observational portrayal is presented here, using various cloud, aerosol, and meteorological datasets, to characterize the widespread nature of winter fog. While the understanding of fog formation is known in the literature, detailed surface observations are needed to help build sophisticated fog forecast and early warning systems to minimize its impact on public safety. Additionally, linkages between the seasonal fog cover, regional meteorology, and increasing air pollution should be further investigated against the backdrop of a changing climate scenario.